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Pony Wheel Problem Journals/Blogs
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Frequent poster 820 posts David Calhoun Frequent poster 820 posts
David Calhoun

Does anyone have a solution for MTH Berkshires and some 2-8-0's with the pony wheels jumping off the track at frogs or diamonds and causing derailments? It's driving me crazy. One minute thewy are sailing along smoothly at scale speed with a few cars and a cabin and the next trip around the layout they derail at every mainline switch and diamond.

I think it's the fact that there is not enough weight forward to keep them on the rails, but I'm at a loss as how to correct the problem if that is it. Any ideas that work? Thanks.

Chief Operating Officer

The Greater Nickel Plate
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HVT Dave Prolific poster 1,211 posts
HVT Dave

Pilot weight

See this thread.  BTW a more common name is front pilot wheels.

https://model-railroad-hobbyist.com/node/36058

Dave

Member of the Four Amigos

 
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Prof_Klyzlr Moderator 7,952 posts
Prof_Klyzlr

Firstly

Dear David,

Quote:

Any ideas that work?

Plenty, but they only "work" if they address the actual problem, which must be conclusively diagnosed first.
(Don't want to waste your time, effort, and possibly risk damaging the model,
deploying a load of blind "it worked for me" hypothesis reccomendations,
which do not actually address the fault condition your specific situation is experiencing...)

Firstly:

- Is the front Pony (UK) / Pilot (US) wheelset gauged properly?
(come to that, are all of the wheels gauged properly, esp the drivers directly behind the pony truck?

Pass the NMRA gauge...)

- is there anything which could be binding the rotation of the wheelset in the truck?
(I recall having a world of pain with a brass PSC front pony truck conversion on a Mantua Mallet. Wheelset sliding = picking the frog and derailing. The end-result diagnostic was an occasional bind of the wheeset rotation in the IF brass truck casting. A quick few passes with a file to narrow/smooth the faces of the truck casting that bore on the backsides of the spoked wheelset as the truck was forced sideways when cornering, and all was well...)

- Is there any binding on the front pony truck swing?
(also note for fouling of any frame or back-of-cyclinder member)

- is there any springing pressing on the front pony truck, which may be slipping out-of-position or causing unwanted mechanical interaction?

Looking towards the environment, does it always derail:

- on the same turnout?
- travelling thru the turnout in the same direction? (Toe --> Heel, or Heel --> Toe?)
- travelling thru the Diverging, the Straight, or BOTH routes of the turnout?
- travelling in the same direction? (Fwd or Bkwd)

- Do other locos derail at the same place/turnout/direction?
(if NO, those reliable locos provide an A/B comparison for all of the gauging and truck-swing checks above)

Rest assured, it's a simple mechanical system,
the root-cause can be found, confirmed, and fixed...

...just gotta diagnose properly first...

Happy Modelling,
Aim to Improve,
Prof Klyzlr
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